The correct choice is
D. 22 Hz and 42 Hz.
In fact, the beat frequency is given by the difference between the frequencies of the two waves:
In this problem, the beat frequency is 
, therefore the only pair of frequencies that gives a difference equal to 20 Hz is
D. 22 Hz and 42 Hz.
Answer:
Sundial is an instrument showing the time by the shadow of a pointer cast by the sun on to a plate marked with the hours of the day.
If the scale is not "zeroed". If you do not use grams (g) to lable your products. If you do not unlock the balance. [that's about all I got doll]
Answer:
Change/ Potential
Explanation:
Work is the amount of energy required to perform an action that is for a force to cause a displacement.
From work-energy theorem, work done by body is equal to change in its kinetic energy.
Work of gravity is basically the potential energy stored in the body due to gravity. From the law of conservation of mechanical energy, increased kinetic energy comes from the change of the potential energy of the stone.
Answer:
Faraday invented the electromagnetic rotation.
Explanation:
Faraday invented a device called electromagnetic rotation, Faraday got a rotation with magnetic force, he used a cable, mercury, and a magnet.
The cable would rotate around the magnet, this would be a beginning for the electromagnetic technology.
For example:
The Homopolar motor or called electric motor was created for Faraday's invention.
We can find electric motor in Washing machines, fans, turbines, even in motorcycles and electric cars.
